Acorlett
A cracking route but you're arguably doing it in the wrong direction!!!!!!! I suspect you will have more carrying doing it clockwise and the descent to Glen Derry from MacDhui gets two thumbs up from some of the other forum dwellers.
I rode the last part of your route the other way last weekend. I'm planning on doing your loop in reverse this weekend and hopefully taking in Cairngorm, MacDhui, Derry Cairngorm and Bynack Mor summits for good measure. The first half of the descent to Etchacan is truly world class and I gather the next section is even better (only walked it in winter in the snow). I don't reckon the descent off MacDhui, although no doubt good, would be as good as the alternative. If you descend from Bynack Mor, you are pretty much downhill all the way to Glenmore Lodge.
I reckon you would have to be pretty fit to do it in 4 to 5 hours with no stops and really cracking along. There's a lot of height gain and loss in that loop. You'll also want to stop to take photos, take in the views and get some food down yer craw!
Messiah is your man for the local advice and in my experience, he calls things spot on.
Cheers
Sanny
PS
Captain Mainwaring
Mealle a Buchaille with the descent down to Ryvoan - very nice indeed. Add in Badaguish and you have a cracking circuit. Just make sure you take pics and post them here!